package org.jaronsource.framework.core.spring;

import org.springframework.core.MethodParameter;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.method.support.ModelAndViewContainer;
import org.springframework.web.servlet.RequestToViewNameTranslator;

/**
 * Handles return values of types {@code void} and {@code String} interpreting them as view name reference.
 * 
 * <p> A {@code null} return value, either due to a {@code void} return type or as the actual return value is left as-is
 * allowing the configured {@link RequestToViewNameTranslator} to select a view name by convention.
 * 
 * <p> A String return value can be interpreted in more than one ways depending on the presence of annotations like
 * {@code @ModelAttribute} or {@code @ResponseBody}. Therefore this handler should be configured after the handlers that
 * support these annotations.
 * 
 * @author Rossen Stoyanchev
 * @since 3.1
 */
public class ViewNameMethodReturnValueHandler implements HandlerMethodReturnValueHandler {

	public boolean supportsReturnType( MethodParameter returnType ) {
		Class<?> paramType = returnType.getParameterType();
		return ( void.class.equals( paramType ) || String.class.equals( paramType ) );
	}

	public void handleReturnValue(	Object returnValue,
									MethodParameter returnType,
									ModelAndViewContainer mavContainer,
									NativeWebRequest webRequest ) throws Exception {
		if ( returnValue == null ) {
			return;
		}
		else if ( returnValue instanceof String ) {
			String viewName = (String) returnValue;
			mavContainer.setViewName( viewName );
			if ( isRedirectViewName( viewName ) ) {
				mavContainer.setRedirectModelScenario( true );
			}
		}
		else {
			// should not happen
			throw new UnsupportedOperationException( "Unexpected return type: " + returnType.getParameterType().getName() + " in method: " + returnType.getMethod() );
		}
	}

	/**
	 * Whether the given view name is a redirect view reference.
	 * 
	 * @param viewName the view name to check, never {@code null}
	 * @return "true" if the given view name is recognized as a redirect view reference; "false" otherwise.
	 */
	protected boolean isRedirectViewName( String viewName ) {
		return viewName.startsWith( "redirect:" ) || viewName.startsWith( "history:" );
	}

}
